A niobium oxide has been broadly used as a material for electronic parts, such as a frequency filter and a capacitor, a target of sputtering, and the like. Especially, when a niobium oxide is used as a dielectric substance for a capacitor, owing to its resistance to damages by load voltage and flame retardancy, a capacitor with high reliability can be produced. Furthermore, owing to its lower density compared with metallic niobium or tantalum of the same volume, downweighting and downsizing of the capacitor are possible, and further owing to a high dielectric constant a capacitor with a high capacitance can be produced. For use in a capacitor, especially niobium monoxide among niobium oxides has attracted the attention.
Methods for producing a niobium oxide by which the particle size or the specific surface area can be regulated have been known as the prior art (Patent Document 1, Patent Document 2). Further a niobium monoxide probably suitable for use in a capacitor has been proposed (Patent Document 3).
Patent Document 1: Japanese Patent Application Laid-Open No. Hei 07-101726
Patent Document 2: Japanese Patent Application Laid-Open No. 2002-321917
Patent Document 3: WO2002/093596
According to Patent Document 1 and Patent Document 2, a niobium oxide with a large specific surface area can be obtained, and in Patent Document 3 a niobium monoxide having a tap density, a specific surface area and the like suitable for use in a capacitor, with a small particle size and high purity is disclosed. In case a capacitor is produced with a niobium monoxide having a high specific surface area, not only the capacitance can be increased, but also impregnation of an electrolytic solution can be advantageously improved.
Due to rapid advancement of miniaturization and slimming down of electronic devices in the recent years, a niobium capacitor being small in size but having large capacitance is now strongly demanded. However, the niobium monoxide, whose specific surface area, tap density, particle size, and the like are specified by the prior art, cannot fully meet the requirements of the market as a raw material for a niobium capacitor. A development of a more suitable material for a capacitor has been desired.
Under such circumstances, an object of the present invention is to provide a niobium monoxide realizing large capacitance with a miniature sized capacitor.